To set something up is to arrange it or establish it so it’s ready to use. For example, I can set up a website, set up a gym membership, set up the furniture in my new house.
To set SOMEBODY up is different. It could mean 3 things.
(1) To make it look like someone has done something wrong, so they will get in trouble.
Example: They set him up by putting stolen goods in his bag. <<That situation is a set up (noun).
(2) To arrange a situation in order to play a prank or a joke on someone.
Example: His friends set him up by telling him it was a costume party, when it wasn’t. He came dressed up as Captain Jack Sparrow to a formal dinner party.
(3) To set somebody up (WITH somebody else) means to arrange for them to meet because you think they would be good together in a relationship.
Example:
A: Where did you meet your wife?
B: A mutual friend set us up.
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